The present invention relates to a fine zeolite particle, a process for preparing the same, and a detergent composition comprising the fine zeolite particle.
Zeolites are crystalline aluminosilicates, which can be classified into various crystal structures such as A-type, X-type and Y-type by the arrangements of SiO4 tetrahedrons and AlO4 tetrahedrons. The zeolites have an even pore size depending upon the crystal structures, thereby exhibiting a molecular sieve function. For the reason, the zeolites have been used for adsorbents, catalysts (carriers) and the like. In addition, since the zeolites have cationic exchange abilities, they have been utilized as detergent builders, agents for waste water treatment, and the like.
The functions of the zeolites greatly depend on the crystal structure and the composition of the zeolite. For instance, the smaller the Si/Al molar ratio of the zeolite, the larger the cationic exchange capacity, and theoretically an A-type zeolite of which Si/Al is 1 is most excellent. Therefore, the A-type zeolites having a high cationic exchange theoretical capacity have been mainly used as detergent builders.
Further, as detergent builders, there are especially needed zeolites excellent in not only the calcium ion exchange capacity but also the calcium ion exchange rate. This is because when calcium ions in water especially at an initial stage of washing can be captured in large amounts, the detergency performance is improved. Since the calcium ion exchange rate of the zeolite is determined by a collision probability of the calcium exchange site of the zeolite with the calcium ions in water, the smaller the primary particle size of the zeolite, the higher the calcium ion exchange rate of the zeolite.
In view of above, various proposals for preparing A-type zeolites having a very small primary particle size have been so far made. For instance, Japanese Patent Laid-Open No. Sho 54-81200 discloses a process for preparing a fine A-type zeolite particle comprising carrying out the reaction in the co-existence of an organic acid such as formic acid or acetic acid in a reaction mixture. However, in this process, the resulting zeolite particle only has a primary particle size of at least 0.5 xcexcm. On the other hand, Japanese Patent Laid-Open No. Hei 1-153514 discloses a process for preparing a fine A-type zeolite particle having a maximal particle size of 0.4 xcexcm or less, comprising forming a zeolite nucleus at a temperature of 40xc2x0 C. or less. However, even in this process, the formed A-type zeolite particle has a primary particle size of at least 0.2 xcexcm.
Meanwhile, a largest defect of the zeolite builder is in that zeolite makes water turbid due to its water insolubility. In view of this problem, there has been proposed to reduce turbidity of the zeolite by making an aggregate particle size of the zeolite small to a size of equal to or less than a wavelength of visible light (0.4 xcexcm) [Okumura, Nendo Kagaku 27, 21 (1987)]. In other words, the turbidity of the washing water is reduced with making the aggregate particle size smaller, and when the aggregate particle size is 0.4 xcexcm or less, the washing water (zeolite concentration: 0.013% by weight) becomes almost transparent. However, when the A-type zeolite of which aggregate particle size is made very fine to the order of submicron size is made into a powdery state, the powder then re-aggregates to undesirably form a large aggregate. Also, it is very difficult to carry out solid-liquid separation for the zeolite by means of filtration or concentration. Therefore, the zeolite has been actually fed to the detergent raw material in a slurry state. At this time, the existence of Al ions in the slurry (unreacted compounds of the zeolite raw materials or zeolite-eluted products) could be a factor of lowering the detergency performance. Therefore, the Al ion concentration in the slurry must be controlled to a low level.
Generally, the aggregate particle size of A-type zeolite is made smaller by means of vigorous stirring, pulverization or the like. For instance, as disclosed in Japanese Patent Laid-Open No. Hei 9-67117, an aggregate particle size and a primary particle size are made smaller to the order of submicron size by mechanical pulverization. However, when an A-type zeolite having a large primary particle size is subjected to pulverization treatment, the cationic exchange abilities, i.e. the cationic exchange capacity and the cationic exchange rate, are undesirably lowered due to the crystallinity degradation caused by the disintegration of primary crystals of the A-type zeolite and the deterioration of the primary particle size distribution. In addition, in a water-based liquid of the zeolite after the pulverization treatment, ions of zeolite-constituting elements, i.e. Al, Si, and Na, especially Al, tend to be easily eluted in water, by the mechanochemical reaction of the zeolite particle surface. Therefore, when the zeolite is used for a detergent composition, there also arises a problem that the detergency performance of the composition is lowered.
In order to suppress the generation of the problems due to the process of making the aggregate particle size of the zeolite smaller, the disintegration of the zeolite primary crystals by the process of making the size fine must be avoided. In order to avoid the disintegration, it is desired that the primary particle size of A-type zeolite before pulverization is equal to or less than the aggregate particle size of the zeolite after pulverization. Concretely, when the average aggregate particle size is made smaller to a size of 0.4 xcexcm or less, the average primary particle size is generally 0.1 xcexcm or less. On the basis of this fact, it is considered to be desirable that the average primary particle size of A-type zeolite before pulverization is 0.1 xcexcm or less in order to suppress the generation of the problems mentioned above and to make the zeolite particle smaller by pulverizing the particle until the particle has an average aggregate particle size (0.4 xcexcm or less) which gives almost transparent washing water (zeolite concentration: 0.013% by weight). In addition, as long as a zeolite has the average primary particle size mentioned above, a desired average aggregate particle size could be obtained without subjecting the zeolite to pulverization treatment. However, as mentioned above, there are no examples of a process for preparing a fine A-type zeolite particle having an average primary particle size of 0.1 xcexcm or less without carrying out pulverization treatment or the like after the reaction for preparing the zeolite.
An object of the present invention is to provide a fine A-type zeolite particle having an average primary particle size of 0.1 xcexcm or less and a variation coefficient of 90% or less, and excellent in the cationic exchange capacity, and giving small amounts of Al eluted in water and little water turbidity in a water-based liquid, a process for preparing the fine A-type zeolite particle, and a detergent composition comprising the fine A-type zeolite particle (hereinafter simply referred to as xe2x80x9cfine zeolite particle or fine zeolite particlesxe2x80x9d), which is very excellent in the detergency and the rinsing performance.
These and other objects of the present invention will be apparent from the following description.
According to the present invention, there is provided:
(1) A fine A-type zeolite particle having an average primary particle size of 0.1 xcexcm or less and a variation coefficient of 90% or less, wherein a ratio of a peak area above a background level to all peak area in the range of 2xcex8=20xc2x0 to 40xc2x0 in a powder X-ray diffraction spectrum of said fine A-type zeolite particle is 30% or more;
(2) a process for preparing the fine A-type zeolite particle of item (1) above, comprising reacting a silica source with an aluminum source in the presence of an organic compound having an oxygen-containing functional group and a molecular weight of 100 or more; and
(3) a detergent composition comprising a surfactant and the fine A-type zeolite particle of item (1) above.
The fine zeolite particle of the present invention can be prepared by reacting a silica source with an aluminum source in the presence of an organic compound having an oxygen-containing functional group and a molecular weight of 100 or more. By carrying out the reaction for preparing the zeolite as described above, the crystal growth of the zeolite can be suppressed, whereby a fine A-type zeolite particle having an average primary particle size of 0.1 xcexcm or less can be formed. In the fine zeolite particle obtained as described above, even if the particle were desirably further made smaller by mechanical pulverization or the like until the particle has an average aggregate particle size of 0.4 xcexcm or less which gives substantially transparent washing water (zeolite concentration: 0.013% by weight), the crystallinity degradation, the deterioration of the average primary particle size distribution and the elution of Al (Al ion) can be suppressed.
Specifically, the fine zeolite particle of the present invention is an A-type zeolite having an average primary particle size of 0.1 xcexcm or less and a variation coefficient of 90% or less. The zeolite is excellent in the cationic excellent abilities, and gives substantially no elution of Al ions into water from the zeolite in a water-based liquid containing the zeolite and little water turbidity of the liquid.
The term xe2x80x9cwater-based liquidxe2x80x9d as referred to herein is a liquid comprising certain components and water as a medium including an aqueous solution, a suspension, a dispersion or the like.
The fine zeolite particle of the present invention has an average primary particle size of 0.1 xcexcm or less, preferably 0.08 xcexcm or less, more preferably 0.05 xcexcm or less. As mentioned above, when the average aggregate particle size is made smaller by pulverization from the viewpoint of improving the turbidity of washing water, there arise some problems such as crystallinity degradation of the zeolite. The extent of generation of the problems depends on the average primary particle size of zeolite before pulverization: The larger the average primary particle size, the more serious the problem. Generally, in a A-type zeolite having an average primary particle size larger than 0.1 xcexcm, the primary crystal itself is disintegrated by pulverization, so that the ions of constituent elements are eluted from the zeolite in large amounts and the crystallinity degradation progresses drastically as mentioned above. Since the fine zeolite particle of the present invention has an average primary particle size within the above-mentioned range, the generation of the problems caused by pulverization would be substantially completely suppressed. The average primary particle size can be determined by the method described in Examples set forth below.
The particle size distribution of the zeolite having the average primary particle size in the range mentioned above can be evaluated by variation coefficient The variation coefficient can be calculated according to the method described in Examples set forth below. The particle size distribution of the fine zeolite particle of the present invention is highly uniform satisfying the variation coefficient of the above-mentioned average primary particle size of 90% or less, preferably 70% or less, more preferably 50% or less, still more preferably 35% or less. In other words, the fine zeolite particle of the present invention is composed of a zeolite having a desired average primary particle size of 0.1 xcexcm or less and a uniform particle size distribution, which contributes to the exhibition of excellent cationic exchange abilities. In an A-type zeolite having a large average primary particle size of 1 xcexcm or more, the state of disintegration of the primary crystals caused by pulverization can be captured by scanning electron microscope, and the variation coefficient of the average primary particle size becomes generally large by the pulverization. On the other hand, in the fine zeolite particle of the present invention, the disintegration of the primary crystals caused by pulverization is substantially completely suppressed, and an aggregate of the primary particles is merely disaggregated during the pulverization. Therefore, the changes in the variation coefficient caused by pulverization do not substantially take place.
The fine zeolite particle of the present invention is an A-type zeolite, which can show substantially the same powder X-ray diffraction pattern as that of a known A-type zeolite (Joint Committee on Powder Diffraction Standards No. 38-241). Here, as long as the powder X-ray diffraction pattern of the fine zeolite particle is substantially the same as that of a known one, the pattern may contain peaks ascribed to other crystalline substances and halo peaks belonging to amorphous substances. In addition, a ratio (powder X-ray diffraction intensity ratio) of a powder X-ray diffraction peak intensity I410 of the fine zeolite particle of the present invention to an I410 of d=0.3 nm belonging to a plane (410) of a commercially available A-type zeolite (for instance, xe2x80x9cTOYOBUILDERxe2x80x9d manufactured by Tosoh Corporation) having an average primary particle size of 1 xcexcm or more is preferably 10% or more, more preferably 20% or more, from the viewpoint of improving the cationic exchange abilities.
In addition, the crystallinity of the fine zeolite particle of the present invention can be evaluated by a ratio (Ar) of a peak area above the background level in all peak area in the range of 2xcex8=20xc2x0 to 40xc2x0 in the powder X-ray diffraction spectrum. The Ar can be concretely calculated by the method described in Examples set forth below. The fine zeolite particle of the present invention has Ar of 30% or more, preferably 33% or more, within which range the proportion of amorphous portions in the primary crystal structure is small, excellent cationic exchange abilities can be exhibited, and the lowering of the detergency performance due to elution of Al ions can be suppressed.
On the other hand, since the Ar shows the crystallinity of the zeolite, an extent of the crystallinity degradation caused by pulverization can be evaluated as a crystallinity degradation ratio on the basis of Ar obtained before and after the pulverization. The crystallinity degradation ratio can be calculated by the method described in Examples set forth below. In the fine zeolite particle of the present invention, the crystallinity degradation ratio is preferably 50% or less, more preferably 40% or less, still more preferably 35% or less, from the viewpoints of keeping primary crystallinity, thereby suppressing the lowering of cationic exchange abilities and the elution of Al ions.
The fine zeolite particle of the present invention has an average aggregate particle size of preferably 0.4 xcexcm or less, more preferably 0.3 xcexcm or less. The average aggregate particle size can be determined by the method described in Examples set forth below. The degree of turbidity by the fine zeolite particle of the present invention can be also determined as turbidity by the method described in Examples set forth below. When the average aggregate particle size is within the range mentioned above, the turbidity can be preferably 30% or less, more preferably 20% or less. When the average aggregate particle size and the turbidity are within the above ranges, in the case, for instance, where the zeolite is added to a detergent composition such as a laundry powdery detergent and a laundry liquid detergent, it is preferable because the water turbidity of washing water and initial rinsing water is remarkably improved so that the water becomes substantially transparent, and a problem that the zeolite remains on a fiber surface does not also take place.
When the fine zeolite particle does not have an average aggregate particle size of 0.4 xcexcm or less as a primary product obtained by the process for preparing the fine zeolite particle of the present invention described below, the fine zeolite particle may be further subjected to pulverization as described below as desired. As described above, since the fine zeolite particle of the present invention has an average primary particle size of 0.1 xcexcm or less, the lowering of primary crystallinity is small even if subjected to appropriate pulverization to give an average aggregate particle size of 0.4 xcexcm or less. Therefore, substantially no problems on the lowering of cationic exchange abilities and on the elution of Al in large amounts take place. In the present invention, it is preferable that the fine zeolite particle obtained as a primary product is appropriately pulverized, from the viewpoint of further improving the transparency of washing water, when the fine zeolite particle of the present invention is used as a detergent builder.
In addition, when the water-based liquid of the fine zeolite particle of the present invention is prepared, the ratio of the amount of Al eluted in water is preferably less than 4% by weight, more preferably 3.5% by weight or less, still more preferably 3.2% by weight or less, of the entire amount of Al contained in the fine zeolite particle. It is preferable that the proportion of the amount of Al eluted is within the range mentioned above, because in the case where the fine zeolite particle is added to, for instance, a detergent composition, the lowering of qualities (detergency performance, storage stability and the like) of the detergent composition can be suppressed. In addition, the lowering of primary crystallinity and the amount of Al eluted are small even if subjected to appropriate pulverization to give an average aggregate particle size within the desired range. The proportion of the amount of Al eluted in water can be determined by the method described in Examples set forth below.
Also, the fine zeolite particle of the present invention is excellent in the cationic exchange abilities. Here, the term xe2x80x9ccationic exchange abilitiesxe2x80x9d refer to both the cationic exchange rate and the cationic exchange capacity. More concretely, the term xe2x80x9ccationic exchange ratexe2x80x9d refers to an amount of Ca which is ion-exchanged per one gram of a zeolite in one minute, and the term xe2x80x9ccationic exchange capacityxe2x80x9d refers to an amount of Ca which is ion-exchanged per one gram of a zeolite in ten minutes. The cationic exchange rate and the cationic exchange capacity can be determined by the methods described in Examples set forth below.
The above-mentioned cationic exchange rate (CER) is preferably 180 mg CaCO3/g or more, more preferably 200 mg CaCO3/g or more, still more preferably 220 mg CaCO3/g or more. On the other hand, the above-mentioned cationic exchange capacity (CEC) is preferably 200 mg CaCO3/g or more, more preferably 210 mg CaCO3/g or more, still more preferably 220 mg CaCO3/g or more. It is preferable that the cationic exchange abilities of the fine zeolite particle of the present invention are within the above ranges, because in a case where the zeolite is used for a detergent composition, the detergency performance of the composition is remarkably improved. In addition, there are little crystallinity degradation and deterioration of particle size distribution even if subjected to appropriate pulverization to give an average aggregate particle size within the desired range. Therefore, there are substantially no changes in the cationic exchange abilities.
The fine zeolite particle of the present invention has a composition, in the anhydride form, represented by the general formula xM2O .ySiO2.Al2O3.zMeO, wherein M is an alkali metal atom, Me is an alkaline earth atom. In the formula, it is preferable that x is from 0.2 to 4, y is from 0.5 to 6, and z is from 0 to 0.2, and it is more preferable that x is from 0.8 to 2, y is from 1 to 3, and z is from 0.001 to 0.1. Those elements other than the elements given in the above compositional formula can be contained in the composition within the range so as not to lower the cationic exchange abilities. The above-mentioned alkali metal atom refers to those elements belonging to Group IA of the Periodic Table, and is not particularly limited. Among the alkali metal atoms, sodium is preferable. The fine zeolite particle of the present invention can contain two or more alkali metal atoms. In addition, the above-mentioned alkaline earth metal atom refers to those elements belonging to Group IIA of the Periodic Table, and is not particularly limited. Among the alkaline earth metal atoms, calcium and magnesium are preferable. The fine zeolite particle of the present invention can contain two or more alkaline earth metal atoms.
Next, the process for preparing a fine zeolite particle of the present invention will be described. One of the greatest features of the process resides in that a silica source is reacted with an aluminum source in the presence of an organic compound having an oxygen-containing functional group and a molecular weight of 100 or more (hereinafter referred to as xe2x80x9ccrystallization inhibitorxe2x80x9d). Since the reaction is carried out in the presence of the crystallization inhibitor, the flowability of the reaction mixture (slurry) comprising a silica source and an aluminum source is increased, thereby improving the reaction efficiency. At the same time, the crystal growth of the zeolite is suppressed, so that the zeolite particle having small average primary particle size and even particle size distribution can be formed.
The mechanism for suppression of the zeolite crystal growth by the coexistence of the above-mentioned crystallization inhibitor is presumably as follows: Silanol (Sixe2x80x94OH) group or the like on the surface of a zeolite nucleus interacts with oxygen atom of the functional group via a hydrogen bonding-like interaction, so that the zeolite nucleus surface is stabilized, thereby suppressing the crystal growth (Ostwald growth). Also, the zeolite nucleus themselves are sterically repulsed due to the steric hindrance of the crystallization inhibitors adsorbed to (interacting with) the zeolite nucleus, whereby the crystal growth by collision of the zeolite nuclei themselves is inhibited. As a result, a fine zeolite particle having a small average primary particle size is formed.
The silica source and the aluminum source which are used in the process for preparing a fine zeolite particle of the present invention are not particularly limited. For instance, as the silica source, a commercially available water glass can be used, and silica rock, silica sand, cristobalite, kaolin, cullets, and the like can be also used. Further, they may be properly diluted with water or an aqueous alkali metal hydroxide upon use. In addition, as the aluminum source, aluminum-containing compounds such as aluminum hydroxide, aluminum sulfate, and aluminum chloride can be used, and powder or a water-based liquid of an alkali metal aluminate, especially sodium aluminate, is preferably used. These compounds may be commercially available products. As the water-based liquid of sodium aluminate, those obtained by dissolving aluminum hydroxide and an alkali metal hydroxide in water with heating can be used.
The crystallization inhibitor has a molecular weight of 100 or more, preferably 200 or more, more preferably 400 or more. When the molecular weight of the crystallization inhibitor is less than 100, there is little steric hindrance of the crystallization inhibitor adsorbed to (interacting with) the zeolite nucleus surface, so that the progress of the crystal growth by collision of the zeolite nuclei themselves cannot be effectively suppressed, whereby a desired crystallization inhibiting effect cannot be obtained. In addition, the molecular weight of the crystallization inhibitor is preferably 60000 or less, more preferably 30000 or less, still more preferably 10000 or less, within which range the crystallization inhibitor is sufficiently dissolved in the reaction mixture comprising a silica source and an aluminum source, so that the amount of the crystallization inhibitor adsorbed to the zeolite nucleus (amount of the crystallization inhibitor interacting with the zeolite nucleus) is increased, whereby a crystallization inhibiting effect is sufficiently exhibited. Especially, the crystallization inhibitor has a molecular weight of preferably from 100 to 60000, more preferably from 200 to 30000, still more preferably from 400 to 10000. In the present invention, when the crystallization inhibitor has one or more hydroxyl groups or one or more carboxyl groups at one end or both ends, the molecular weight of the crystallization inhibitor can be determined by quantitative analysis of functional groups, for instance, the analysis of hydroxyl value or acid value. In addition, for instance, when the molecular weight is 1000 or more, the molecular weight is a weight-average molecular weight, which can be determined by GPC (gel permeation chromatography) in accordance with a known method.
The functional group of the crystallization inhibitor is not particularly limited, as long as it contains oxygen atom. The preferable oxygen-containing functional group includes, for instance, OR group, COOR group, SO3R group, PO4R group, CO group, CONH group, and the like, among which OR group and/or COOR group is more preferable. R is at least one member selected from a saturated or unsaturated organic group having 1 to 22 carbon atoms, hydrogen atom and an alkali metal atom. The saturated or unsaturated organic group having 1 to 22 carbon atoms includes, for instance, ethylene group, vinyl group, phenyl group, hexyl group, dodecyl group, and the like. The alkali metal atom includes, for instance, sodium, potassium, and the like. These functional groups may construct a main chain, or they may construct a side chain. The number of functional groups per one molecule of the crystallization inhibitor is not particularly limited. The number of functional groups per one molecule is preferably 2 or more, more preferably 3 or more, still more preferably 4 or more. It is preferable that the number of functional groups per one molecule is within the above range, from the viewpoint of giving a sufficient number of interaction site of the zeolite nucleus and the crystallization inhibitor, thereby giving an excellent crystallization inhibiting effect of the zeolite. In addition, the number of functional groups per one molecule is preferably 1000 or less, more preferably 500 or less, still more preferably 200 or less. It is preferable that the number of functional groups per one molecule is within the above range, from the viewpoints of giving appropriate molecular weight of the crystallization inhibitor for sufficiently dissolving the compound in a reaction mixture, whereby exhibiting an excellent crystallization inhibiting effect.
Concrete examples of the crystallization inhibitor include nonionic surfactants such as polyoxyethylene lauryl ether; and water-soluble polymers such as polyethylene glycol, polyvinyl alcohols, acrylate-based polymers, carboxymethyl cellulose and hexametaphosphate; and the like, without being limited thereto. These compounds can be used as a mixture of two or more kinds.
The feeding composition for preparing the fine zeolite particle of the present invention, as expressed by an SiO2/Al2O3 molar ratio, is preferably 0.5 or more, more preferably 1 or more, still more preferably 1.5 or more. It is preferable that the SiO2/Al2O3 molar ratio is within the above range, from the viewpoints of stabilizing the crystal structure of the zeolite, thereby suppressing the lowering of crystallinity, and accelerating the progress of crystallization. In addition, the SiO2/Al2O3 molar ratio is preferably 4 or less, more preferably 3 or less, still more preferably 2.5 or less. It is preferable that the SiO2/Al2O3 molar ratio is within the above range, from the viewpoints of favorably progressing the reaction, thereby giving sufficient cationic exchange abilities.
Also, the feeding composition of the compound containing an alkali metal, as expressed by an M2O/Al2O3 molar ratio, the alkali metal (M) being shown as an oxide, is preferably 0.08 or more, more preferably 0.8 or more, still more preferably 1.4 or more. It is preferable that the M2O/Al2O3 molar ratio is within the above range, from the viewpoint of accelerating the progress of crystallization. In addition, the M2O/Al2O3 molar ratio is preferably 20 or less, more preferably 5 or less, still more preferably 3 or less. It is preferable that the M2O/Al2O3 molar ratio is within the above range, from the viewpoint of favorable productivity.
Further, the feeding composition of the compound containing an alkali metal and water in the reaction system, as expressed by an M2O/H2O molar ratio, is preferably 0.02 or more, more preferably 0.05 or more, still more preferably 0.07 or more. It is preferable that the M2O/H2O molar ratio is within the above range, from the viewpoint of giving an appropriate crystallization rate, thereby favorably progressing the formation of the fine zeolite particle with small average primary particle size. In addition, the M2O/H2O molar ratio is preferably 0.2 or less, more preferably 0.15 or less, still more preferably 0.1 or less. It is preferable that the M2O/H2O molar ratio is within the above range, from the viewpoint of properly progressing the reaction, thereby giving sufficient cationic exchange abilities.
Furthermore, the feeding composition of the compound containing an alkaline earth metal, as expressed by an MeO/Al2O3 molar ratio, the alkaline earth metal (Me) being shown as an oxide, is preferably 0 to 0.1. The MeO/Al2O3 molar ratio is more preferably 0.005 or more, still more preferably 0.01 or more, from the viewpoints of accelerating making the average primary particle size fine and improving thermal stability. In addition, the MeO/Al2O3 molar ratio is preferably 0.1 or less, more preferably 0.08 or less, still more preferably 0.05 or less, from the viewpoint of improving the ion exchange abilities.
Moreover, the feeding composition of the aluminum in the reaction system, as expressed by an Al2O3/H2O molar ratio, is preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more. It is preferable that the Al2O3/H2O molar ratio is within the above range, from the viewpoints of excellent productivity and acceleration of making the average primary particle size fine. In addition, the Al2O3/H2O molar ratio is preferably 0.25 or less, more preferably 0.2 or less, still more preferably 0.1 or less. It is preferable that the Al2O3/H2O molar ratio is within the above range, from the viewpoint of giving an excellent flowability to the slurry, thereby efficiently progressing the reaction.
When the solid content is defined as a total weight of each inorganic element contained in the raw materials used constituting the fine zeolite particle of the present invention calculated as an oxide, and the concentration of the solid content during the reaction is defined as the concentration of the solid content in the entire water-containing slurry, the concentration of the solid content is preferably 10% by weight or more, more preferably 20% by weight or more, still more preferably 30% by weight or more, from the viewpoint of productivity In addition, the concentration of the solid content is preferably 70% by weight or less, more preferably 60% by weight or less, still more preferably 50% by weight or less, from the viewpoint of the flowability of the slurry.
On the other hand, the feeding amount of the above-mentioned crystallization inhibitor is preferably 1% by weight or more, more preferably 5% by weight or more, still more preferably 10% by weight or more, in the reaction mixture comprising a silica source and an aluminum source, from the viewpoint of exhibiting a crystallization inhibiting effect. In addition, the feeding amount of the above-mentioned crystallization inhibitor is preferably 80% by weight or less, more preferably 60% by weight or less, still more preferably 50% by weight or less, from the viewpoint of productivity.
The fine zeolite particle of the present invention is, for instance, prepared by feeding a silica source, an aluminum source and a crystallization inhibitor each in a separate vessel, and properly mixing these components in accordance with a known method to react the components. During the reaction, other components may be added within the range so as not to hinder the preparation of the fine zeolite particle of the present invention. Such other components include, for instance, calcium chloride, magnesium chloride and the like. It is preferable that each of the silica source, the aluminum source and the crystallization inhibitor is fed to the reaction in the form of water-based liquid, from the viewpoint of homogeneously and efficiently carrying out the reaction.
The mixing order of the silica source, the aluminum source and the crystallization inhibitor is not particularly limited. A liquid mixture of the aluminum source and the crystallization inhibitor may be mixed with the silica source, or a liquid mixture of the silica source and the crystallization inhibitor may be mixed with the aluminum source. Alternatively, the silica source and the aluminum source may be simultaneously fed to the crystallization inhibitor, and mixed; or the crystallization inhibitor may be previously mixed with the silica source and/or the aluminum source, and the silica source is then mixed with the aluminum source.
In addition, the mixing method is not particularly limited. For instance, the silica source, the aluminum source and the crystallization inhibitor may be subjected to line-mixing, with circulating the silica source, the aluminum source and the crystallization inhibitor together in a specified circulation line. Alternatively, the silica source, the aluminum source and the crystallization inhibitor may be mixed in a reaction vessel (batch-type mixing). The reaction time is not particularly limited because it depends upon the reaction temperature. The reaction time is preferably 30 seconds or more, more preferably 1 minute or more, still more preferably 5 minutes or more, from the termination of adding all the feeding components, from the viewpoint of the homogeneity of reaction. Also, the reaction time is preferably 120 minutes or less, more preferably 60 minutes or less, still more preferably 30 minutes or less, from the viewpoint of productivity.
The reaction temperature is preferably 10xc2x0 C. or more, more preferably 20xc2x0 C. or more, still more preferably 40xc2x0 C. or more. It is preferable that the reaction temperature is within the range specified above, from the viewpoints of giving excellent flowability of the reaction mixture and carrying out homogeneous reaction. Also, the reaction temperature is preferably 100xc2x0 C. or less, more preferably 90xc2x0 C. or less, still more preferably 80xc2x0 C. or less. It is preferable that the reaction temperature is within the range specified above, from the viewpoints of proper energy load and an economical advantage on an industrial scale.
The crystallization can be carried out by aging the reaction mixture after the reaction at a temperature equal to or higher than the reaction temperature under stirring. The aging temperature is not particularly limited. The aging temperature is preferably 50xc2x0 C. or more, more preferably 70xc2x0 C. or more, still more preferably 80xc2x0 C. or more, from the viewpoint of the crystallization rate. In addition, the aging temperature is preferably 120xc2x0 C. or less, more preferably 100xc2x0 C. or less, still more preferably 90xc2x0 C. or less, from the viewpoints of energy load and pressure resistance of the reaction vessel. Although the aging time depends upon the aging temperature, the aging time is preferably 1 minute or more, more preferably 10 minutes or more, still more preferably 30 minutes or more, from the viewpoint of sufficiently carrying out the crystallization. In addition, the aging time is preferably 300 minutes or less, more preferably 180 minutes or less, still more preferably 120 minutes or less, from the viewpoints of the lowering of cationic exchange abilities caused by by-product reaction of sodalite and the productivity.
After the termination of aging, the crystallization is terminated by cooling, diluting or filtering and washing the slurry, or neutralizing the slurry by adding an acid. In the case of filtering and washing the slurry, it is preferable that washing is carried out until pH of the washing preferably becomes 12 or less. Also, in the case of neutralizing the slurry, the acid used for the neutralization is not particularly limited, and sulfuric acid, hydrochloric acid, nitric acid, carbon dioxide gas, oxalic acid, citric acid, tartaric acid, fumaric acid, succinic acid and the like can be used. Sulfuric acid and carbon dioxide gas are preferable, from the viewpoints of preventing corrosion of the devices and lowering costs. It is preferable that the pH of the slurry is adjusted to 8 to 12. After the termination of the crystallization, the fine zeolite particle of the present invention in the form of slurry is obtained. Further, this slurry may be appropriately subjected to filtration or centrifugation to separate zeolite precipitates, and the precipitates are further washed and dried into the form of cake or powder.
Next, the fine zeolite particle obtained as a primary product may be pulverized as desired, from the viewpoint of adjusting the zeolite particle to show a desired average aggregate particle size. The pulverization may be carried out by directly subjecting the slurry of the above-mentioned fine zeolite particle to wet pulverization, or alternatively re-dispersing the resulting fine zeolite particle in a solvent, and thereafter subjecting the dispersion to wet pulverization, or alternatively subjecting a powdery fine zeolite particle to dry pulverization. Each of the pulverization methods can be carried out in accordance with a known method.
For instance, when the fine zeolite particle of the present invention is added to the detergent composition of the present invention described below, the zeolite particle may be added in a slurry form. In this case, it is preferable to carry out wet pulverization, from the viewpoint of simplicity in the preparation steps. The pulverization method employed herein is not particularly limited. For instance, there may be employed pulverizers and the like described in Kagaku Kogakukai Edited, Kagaku Kogaku Binran (published by Maruzen Publishing, 1988), Fifth Edition, pages 826 to 838. Also, the dispersion medium to be used for wet pulverization includes water, alcohol solvents such as ethanol, surfactants such as polyoxyethylene alkyl ethers, polymer dispersants, and the like. They can be used alone or as a mixed solution of two or more kinds. When the slurry is subjected to wet pulverization, the zeolite concentration in the slurry is preferably 5% by weight or more, more preferably 10% by weight or more, still more preferably 15% by weight or more, from the viewpoint of productivity. In addition, the zeolite concentration in the slurry is preferably 60% by weight or less, more preferably 55% by weight or less, still more preferably 50% by weight or less, from the viewpoint of the handleability of the zeolite slurry during the wet pulverization and from the viewpoint of prevention of the re-aggregation of the fine zeolite particle after pulverization.
The fine zeolite particle of the present invention is suitably used for, for instance, detergent builders, water treatment agents, fillers for paper, resin fillers, oxygen-nitrogen separating agents, adsorbents, catalyst carriers, soil improvers for gardening, polishing agents, and the like, and especially preferably used as detergent builders.
Further, the detergent composition of the present invention will be described. The detergent composition comprises a surfactant and the fine zeolite particle of the present invention. Owing to the high cationic exchange abilities, the low Al ion-eluting property and further the low turbidity of the zeolite, the detergent composition exhibits excellent detergency performance and makes rinsing water substantially not turbid, so that the amount of water and the time required for rinsing can be remarkably shortened.
The content of the fine zeolite particle in the detergent composition of the present invention is not particularly limited. The content of the fine zeolite particle in the detergent composition is preferably 1% by weight or more, more preferably 3% by weight or more, still more preferably 5% by weight or more, from the viewpoint of exhibiting satisfactory detergency performance. In addition, the content of the fine zeolite particle is preferably 60% by weight or less, more preferably 50% by weight or less, still more preferably 40% by weight or less, from the viewpoint of stability in the production of the detergent composition. The content of the fine zeolite particle in the detergent composition is preferably from 1 to 60% by weight, more preferably from 3 to 50% by weight, still more preferably from 5 to 40% by weight. In addition, in the detergent composition of the present invention, there may be formulated other known zeolites together with the fine zeolite particle of the present invention. Such other zeolites may be commercially available zeolites, and the crystal structure of such zeolites may be P-type, X-type and the like other than the A-type. Also, the zeolites may be a mixture of two or more of these zeolites. The average primary particle size and the average aggregate particle size of the other zeolite are not particularly limited. The average primary particle size is preferably 10 xcexcm or less, more preferably 5 xcexcm or less, still more preferably 2 xcexcm or less, from the viewpoint of the cationic exchange rate. Also, the average aggregate particle size is preferably 15 xcexcm or less, more preferably 10 xcexcm or less, still more preferably 5 xcexcm or less, from the viewpoint of the dispersibility in water. The proportion of the fine zeolite particle of the present invention contained in all the zeolite used is preferably 10% by weight or more, more preferably 20% by weight or more, still more preferably 50% by weight or more, from the viewpoint of securing the exhibition of the desired effect of the detergent composition of the present invention.
The surfactant to be added to the detergent composition of the present invention is not particularly limited. For instance, there can be exemplified nonionic, anionic, cationic and amphoteric surfactants.
Concrete examples of the nonionic surfactants include those known nonionic surfactants disclosed in xe2x80x9cChapter 3, Section 1 of Shuchixe2x80xa2Kanyo Gijutsushu (Iryoyo Funmatsusenzai) [Known and Well Used Technical Terminologies (Laundry Powder Detergent)]xe2x80x9d a publication made by the Japanese Patent Office. Other nonionic surfactants include polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkylamines, sucrose fatty acid esters, glycerol fatty acid monoesters, higher fatty acid alkanolamides, polyoxyethylene higher fatty acid alkanolamides, amine oxides, alkyl glycosides, alkyl glyceryl ethers, N-alkyl gluconamides and the like.
Examples of the anionic surfactants include those known anionic surfactants disclosed in xe2x80x9cChapter 3, Section 1 of Shuchixe2x80xa2Kanyo Gijutsushu (Iryoyo Funmatsusenzai) [Known and Well Used Technical Terminologies (Laundry Powder Detergent)]xe2x80x9d a publication made by the Japanese Patent Office. The counter ions for the anionic surfactant are selected from the group consisting of sodium ion, potassium ion, magnesium ion, calcium ion, a cation formed by protonating an amine such as ethanolamines, a quaternary ammonium salt, and mixtures thereof.
Examples of the cationic surfactants include those known cationic surfactants disclosed in xe2x80x9cChapter 3, Section 1 of Shuchixe2x80xa2Kanyo Gijutsushu (Iryoyo Funmatsusenzai) [Known and Well Used Technical Terminologies (Laundry Powder Detergent)]xe2x80x9d a publication made by the Japanese Patent Office.
Examples of the amphoteric surfactants include those known amphoteric surfactants disclosed in xe2x80x9cChapter 3, Section 1 of Shuchixe2x80xa2Kanyo Gijutsushu (Iryoyo Funmatsusenzai) [Known and Well Used Technical Terminologies (Laundry Powder Detergent)]xe2x80x9d a publication made by the Japanese Patent Office.
The above-mentioned surfactants can be used alone or in admixture of two or more kinds. In addition, the surfactants can be selected from those of the same or different kinds.
The content of the surfactant in the detergent composition of the present invention is not particularly limited. The content of the surfactant in the detergent composition is preferably 1% by weight or more, more preferably 5% by weight or more, still more preferably 10% by weight or more, from the viewpoint of detergency. Also, the content of the surfactant is preferably 90% by weight or less, more preferably 70% by weight or less, still more preferably 60% by weight or less, from the viewpoint of the productivity of the detergent composition. The content of the surfactant in the detergent composition of the present invention is preferably from 1 to 90% by weight, more preferably from 5 to 70% by weight, still more preferably from 10 to 60% by weight.
In the detergent composition of the present invention, besides the above-mentioned surfactant and the fine zeolite particle of the present invention, there can be properly added various additives which are usually added to laundry detergents. The content of these additives can be properly adjusted as long as they do not inhibit the desired effects of the detergent composition of the present invention.
The above-mentioned additives include, for instance, other inorganic builders, organic builders, enzymes, re-deposition preventives, fluorescers, viscosity-controlling agents, solvents, bleaching agents, dispersing agents, perfume, and the like. The inorganic builder besides the zeolite includes silicates, carbonates, sulfates, sulfites, condensed phosphates, sodium chloride, and the like, and these salts are preferably formed with an alkali metal. The organic builder includes organic alkalizing agents such as alkanolamines such as triethanolamine, diethanolamine and monoethanolamine; organic cation-exchanging agents such as aminopolyacetates such as ethylenediaminetetraacetate, oxycarboxylates such as citric acid, polycarboxylates such as polyacrylic acids and acrylic acid-maleic acid copolymers, and the like, and these salts are preferably formed with an alkali metal or ammonium. The enzyme includes cellulase, amylase, cannase, lipase, protease, and the like. The re-deposition agent includes polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose, and the like. The viscosity-controlling agent and the solvent include lower alcohols such as isopropanol, glycols such as ethylene glycol, glycerol, and the like. The bleaching agent includes inorganic peroxide bleaching agents such as sodium percarbonate and sodium perborate, or a mixture of these inorganic peroxide bleaching agents with a bleaching activator. Examples of the bleaching activator include an organic compound having a reactive acyl group for forming an organic peroxide. Concrete examples of the bleaching activator include sodium lauroyloxybenzenesulfonate, sodium decanoyloxybenzenesulfonate, lauroyloxybenzoic acid, decanoyloxybenzoic acid and the like. Besides them, bleaching activating catalysts such as manganese, cobalt and iron complexes can be added as a bleaching activator.
The detergent composition of the present invention can be obtained by mixing and stirring each of the components mentioned above according to a known method, and thereafter optionally subjecting the resulting mixture to such a treatment as granulation. Since the composition comprises the fine zeolite particle of the present invention, the composition is very excellent in the detergency and the rinsing performance. The detergency and the rinsing performance can be evaluated by the methods described in Examples set forth below.
The determination values of the sample properties in Examples and Comparative examples were measured according to the method set forth below. Here, xe2x80x9c%xe2x80x9d means xe2x80x9c% by weightxe2x80x9d unless otherwise noted. In the table, the units for the cationic exchange abilities are each simply expressed as xe2x80x9cmg/g.xe2x80x9d
(1) Average Primary Particle Size
The primary particle size of zeolite particle for 100 or more particles is measured by a digitizer (commercially available from GRAPHTEC CORPORATION, xe2x80x9cDIGITIZER KW3300xe2x80x9d), on the basis of the scanning electron photomicrographs of a sample zeolite taken by a field-emission high resolution scanning electron microscope (FE-SEM, commercially available from Hitachi Ltd., S-4000). The number-average value (average primary particle size) and the variation coefficient (%) are calculated on the basis of the entire resulting determination values as population. Here, the variation coefficient is calculated by the following equation:                     Variation                                      Coefficient          ⁢                      xe2x80x83                    ⁢                      (            %            )                                =                    Standard        ⁢                  xe2x80x83                ⁢        Deviation        ⁢                  xe2x80x83                ⁢                  (          µm          )                            Average        ⁢                  xe2x80x83                ⁢        Primary        ⁢                  xe2x80x83                ⁢        Particle        ⁢                  xe2x80x83                ⁢        Size        ⁢                  xe2x80x83                ⁢                  (          µm          )                      xc3x97    100  
(2) Powder X-ray Diffraction
The powder sample is subjected to powder X-ray diffraction at room temperature (20xc2x0 C.) by using a powder X-ray diffractometer, commercially available from Rigaku Denki, xe2x80x9cRINT 2500 VPCxe2x80x9d (light source: CuKxcex1 ray, tube voltage: 40 kV, and tube electric current: 120 mA) under the conditions of a scanning interval of 0.01xc2x0 in the range of 2xcex8=5xc2x0 to 40xc2x0, a scanning speed of 10xc2x0/minute, a divergence vertical limiting slit of 10 mm, a divergence slit of 1xc2x0, a light-intercepting slit of 0.3 mm, and a scattering slit being automatic. With taking background level points at 2xcex8=20xc2x0, 28.5xc2x0, 37xc2x0 and 40xc2x0, a background curve is drawn by third-order polynomial, and a peak area Apeak, an area formed between the diffraction curve in the range of 2xcex8=20xc2x0 to 40xc2x0 and the background curve is determined. Ar, which is a proportion of a peak area (Apeak) above the background level in all peak area (Aall) in the range of 2xcex8=20xc2x0 to 40xc2x0 is calculated from the peak area and all the peak area as follows:             A      r        ⁢          xe2x80x83        ⁢          (      %      )        =                    A        peak                    A        all              xc3x97    100  
The term xe2x80x9call peak areaxe2x80x9d refers to an area formed between the diffraction curve in the range of 2xcex8=20xc2x0 to 40xc2x0 and a straight line of intensity zero. In addition, the crystallinity degradation ratio by pulverization is calculated by the following equation:                                                         Crystallinity                                                          Degradation                                                                    Ratio          ⁢                      xe2x80x83                    ⁢                      (            %            )                                =                    1        -                  (                                    A              r                        ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            Zeolite            ⁢                          xe2x80x83                        ⁢            After            ⁢                          xe2x80x83                        ⁢            Pulverization                    )                            (                              A            r                    ⁢                      xe2x80x83                    ⁢          of          ⁢                      xe2x80x83                    ⁢          Zeolite          ⁢                      xe2x80x83                    ⁢          Before          ⁢                      xe2x80x83                    ⁢          Pulverization                )              xc3x97    100  
Further, the powder X-ray diffraction intensity ratio (%) is calculated as a ratio of a powder X-ray diffraction peak intensity (I410) having a face distance d=0.3 nm belonging to a face (I410) of A-type zeolite obtained for the zeolite to be analyzed to I410 of a commercially available A-type zeolite (xe2x80x9cTOYOBUILDER,xe2x80x9d commercially available from TOSOH CORPORATION, I410=32837 cps) having an average primary particle size of 1 xcexcm or more.
(3) Average Aggregate Particle Size
The particle size distribution is measured with a slurry prepared by dispersing a sample in water as a dispersion medium under conditions of a refractive index of 1.2, an ultrasonic intensity of 7, an ultrasonication irradiation time of 1 minute, and a flow rate of 4, using a laser diffraction/scattering particle size distribution analyzer (commercially available from HORIBA Ltd., LA-920). The median diameter (calculated on the basis of volume) obtained is considered as an average aggregate particle size (xcexcm).
(4) Cationic Exchange Capacity
The amount 0.2 g of a water-based liquid of 20% zeolite is added to 100 mL of an aqueous calcium chloride (100 ppm calcium concentration, calculated as CaCO3), and stirred at 20xc2x0 C. for 1 minute or 10 minutes, and the mixture is filtered with a disposable filter with 0.2 xcexcm pore size. Thereafter, 10 mL of the resulting filtrate is taken and assayed for a Ca content in the filtrate by using a photometric titration apparatus, and cationic exchange abilities are determined. Incidentally, the Ca content (calculated as the amount of CaCO3) ion-exchanged per 1 g of the zeolite in 1 minute is referred to as xe2x80x9ccationic exchange rate (CER, expressed as mg CaCO3/g)xe2x80x9d, and the Ca content (calculated as the amount of CaCO3) ion-exchanged per 1 g of the zeolite in 10 minutes is referred to as xe2x80x9ccationic exchange capacity (CEC, expressed as mg CaCO3/g).xe2x80x9d
(5) Turbidity
The turbidity (%) of a water-based liquid of zeolite (zeolite concentration: 0.013%) prepared by stirring the zeolite in water having water hardness of 4xc2x0 at room temperature (20xc2x0 C.) for 10 minutes is determined by using a turbidimeter commercially available from Murakami Color Research Laboratory, reflectance-transmittance meter HR-100.
(6) Detergency
Forty grams of a crystalline silicate (KWS-2, particle size: 11 xcexcm, commercially available from Kao Corporation) is added to a mixed solution of 24.8 g of a nonionic surfactant (EMULGEN 108, commercially available from Kao Corporation), 14.8 g of a polyoxyethylene phenyl ether (commercially available from Nippon Nyukazai) and 0.4 g of a polymer-type dispersant (AQUALOCK FC 600S, commercially available from NIPPON SHOKUBAI CO., LTD.), and the resulting mixture is homogeneously mixed with stirring. The resulting silicate-containing liquid mixture is placed in a 1-L batch-type sand-mill (commercially available from IMEX) together with 500 g of zirconia beads (diameter: 1 mm), and subjected to pulverization at a disc rotational speed of 1500 rpm for 60 minutes. Next, 0.3333 g of a liquid mixture containing the silicate after the pulverization (particle size: 2.3 xcexcm) and 0.3333 g of a water-based liquid of zeolite (zeolite concentration: 20%) are mixed, to give a detergent composition. Five pieces of artificially soiled cloths are washed by washing with the resulting detergent composition for 10 minutes, rinsing for 1 minute and drying using a turg-O-meter (120 rpm, commercially available from Ueshima Seisakusho) in 1 L of water having water hardness of 4xc2x0 at a water temperature of 20xc2x0 C., and the deterging rate (%) is determined. Here, the deterging rate is determined by measuring the reflectances at 550 nm of an unsoiled cloth and the artificially soiled cloth before and after washing by an automatic recording calorimeter (commercially available from Shimadzu Corporation), and calculated by the following equation.                     Deterging                                      Rate          ⁢                      xe2x80x83                    ⁢                      (            %            )                                =                                                        [                                                Reflectance                  ⁢                                      xe2x80x83                                    ⁢                  After                  ⁢                                      xe2x80x83                                    ⁢                  Washing                                -                                                                                                        Reflectance                ⁢                                  xe2x80x83                                ⁢                Before                ⁢                                  xe2x80x83                                ⁢                Washing                            ]                                                                                      [                                                Reflectance                  ⁢                                      xe2x80x83                                    ⁢                  of                  ⁢                                      xe2x80x83                                    ⁢                  Unsoiled                  ⁢                                      xe2x80x83                                    ⁢                  Cloth                                -                                                                                                        Reflectance                ⁢                                  xe2x80x83                                ⁢                Before                ⁢                                  xe2x80x83                                ⁢                Washing                            ]                                            xc3x97    100  
The deterging rate is obtained as an average of 5 pieces of cloths.
The artificially soiled cloths described above are prepared by smearing a cloth (#2003 calico, commercially available from Tanigashira Shoten) with an artificial soil solution having the following composition. The smearing of the cloths with the artificial soil solution is carried out using a gravure roll coater (cell capacity: 58 cm, coating speed: 1 m/minute, drying temperature: 100xc2x0 C., and drying time: 1 minute) made in accordance with Japanese Patent Laid-Open No. Hei 7-270395.
(Composition of Artificial Soil Solution)
The composition of the artificial soil solution is as follows: Lauric acid: 0.44%, myristic acid: 3.09%, pentadecanoic acid: 2.31%, palmitic acid: 6.18%, heptadecanoic acid: 0.44%, stearic acid: 1.57%, oleic acid: 7.75%, triolein: 13.06 /o, n-hexadecyl palmitate: 2.18%, squalene: 6.53%, liquid crystalline product of lecithin, from egg yolk (commercially available from Wako Pure Chemical Industries): 1.94%, Kanuma red clay for gardening: 8.11%, carbon black (commercially available from Asahi Carbon.): 0.01%, and tap water: balance.
(7) Rinsing Performance
Using a detergent composition prepared by mixing a zeolite 22%, a crystalline silicate (SKS-6, particle size: 26 xcexcm, commercially available from Clariant) 11%, and a nonionic surfactant (EMULGEN 108, commercially available from Kao Corporation) 67%, the clothes are washed for 10 minutes under the conditions of a liquor ratio of 1/20, a concentration of the detergent composition of 20 g/30 L, and a water temperature of 20xc2x0 C. in tap water having water hardness of 4xc2x0, and then rinsed for 4 minutes at a rinsing flow rate of 15 L/minute, using a twin-tub washing machine commercially available from TOSHIBA CORPORATION, xe2x80x9cGINGA 3.6xe2x80x9d. Thereafter, the transparency of the rinsing is visually confirmed, and the rinsing performance is evaluated on the basis of the following evaluation criteria. Specifically, after the clothes in the washtub are moved to the side wall of the washtub after stopping the washing machine, the rinsing performance is evaluated on the basis of the 3 grade-evaluation criteria:
◯: the case where the rinsing is transparent, and the pulsator at the bottom of the washtub is clearly seen;
xcex94: the case where the rinsing is slightly turbid, but the pulsator can be seen; and
xc3x97: the case where the rinsing is turbid and the contour of the pulsator cannot be clearly seen.